Spindle advice, foam milling

Hi everyone, I’m looking for your suggestions for spindle specs to mill foam molds out of low density insulation foam.
Machine is custom made, can cut 1m x 35cm x 15cm. Speed is not a requirement as my projects will be small in size and I’d like to keep the budget low.
I’d like to be able to run long reach ball end bits to be able to keep steep sides to the mold sides.
I’m struggling with finding a spindle that would turn slow enough not to melt the foam and as to what power I actually need.. seems way overkill to have a 1.5k spindle just to mill foam.. foam only it will be, my machine actually has capability for metal as well but that’s mounted on a different Z axis/different spindle etc..
Thanks for your help